Biology Reference
In-Depth Information
BOX 3: HOW TO CALCULATE TIMELINESS—CORRELATION
1.
Construct a time series for each data source
a. Plot the frequency (number of cases) on the y-axis
b. Plot time on the x-axis. Time can be recorded by day, date, month, etc.
A
B
Time
2.
Calculate the correlation between the two time series. is will determine the
correlation at zero lag.
3.
Move one data source along the x-axis for a period of time, for example, 7 days.
4.
Calculate the correlation between the two time series. is will determine the
correlation at 7 days lag.
5.
Repeat the above steps for each time lag to be calculated.
6.
Plot time lag (x-axis) against the calculated correlation coecients (y-axis).
7.
Identify on the plot the maximum correlation for the two time series.
Time
Time Lag = n days
8.
e timeliness is quoted as the time lag when the correlation is at a maximum
a. Timeliness A = Time lag (n)
